cxl/region: Store root decoder in struct cxl_region

A region is always bound to a root decoder. The region's associated
root decoder is often needed. Add it to struct cxl_region.

This simplifies the code by removing dynamic lookups and the root
decoder argument from the function argument list where possible.

Patch is a prerequisite to implement address translation which uses
struct cxl_region to store all relevant region and interleaving
parameters. It changes the argument list of __construct_region() in
preparation of adding a context argument. Additionally the arg list of
cxl_region_attach_position() is simplified and the use of
to_cxl_root_decoder() removed, which always reconstructs and checks
the pointer. The pointer never changes and is frequently used. Code
becomes more readable as this amphazises the binding between both
objects.

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Robert Richter <rrichter@amd.com>
Link: https://patch.msgid.link/20260114164837.1076338-3-rrichter@amd.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Author: Robert Richter

drivers/cxl/core/region.c

@@ -489,9 +489,9 @@ static ssize_t interleave_ways_store(struct device *dev,
 				     struct device_attribute *attr,
 				     const char *buf, size_t len)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
-	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
 	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
+	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
 	struct cxl_region_params *p = &cxlr->params;
 	unsigned int val, save;
 	int rc;
@@ -552,9 +552,9 @@ static ssize_t interleave_granularity_store(struct device *dev,
 					    struct device_attribute *attr,
 					    const char *buf, size_t len)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
-	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
 	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
+	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
 	struct cxl_region_params *p = &cxlr->params;
 	int rc, val;
 	u16 ig;
@@ -628,7 +628,7 @@ static DEVICE_ATTR_RO(mode);
 
 static int alloc_hpa(struct cxl_region *cxlr, resource_size_t size)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_region_params *p = &cxlr->params;
 	struct resource *res;
 	u64 remainder = 0;
@@ -1373,7 +1373,7 @@ static int cxl_port_setup_targets(struct cxl_port *port,
 				  struct cxl_region *cxlr,
 				  struct cxl_endpoint_decoder *cxled)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	int parent_iw, parent_ig, ig, iw, rc, pos = cxled->pos;
 	struct cxl_port *parent_port = to_cxl_port(port->dev.parent);
 	struct cxl_region_ref *cxl_rr = cxl_rr_load(port, cxlr);
@@ -1731,10 +1731,10 @@ static int cxl_region_validate_position(struct cxl_region *cxlr,
 }
 
 static int cxl_region_attach_position(struct cxl_region *cxlr,
-				      struct cxl_root_decoder *cxlrd,
 				      struct cxl_endpoint_decoder *cxled,
 				      const struct cxl_dport *dport, int pos)
 {
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
 	struct cxl_switch_decoder *cxlsd = &cxlrd->cxlsd;
 	struct cxl_decoder *cxld = &cxlsd->cxld;
@@ -1971,7 +1971,7 @@ static int cxl_region_sort_targets(struct cxl_region *cxlr)
 static int cxl_region_attach(struct cxl_region *cxlr,
 			     struct cxl_endpoint_decoder *cxled, int pos)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct cxl_region_params *p = &cxlr->params;
@@ -2076,8 +2076,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 			ep_port = cxled_to_port(cxled);
 			dport = cxl_find_dport_by_dev(root_port,
 						      ep_port->host_bridge);
-			rc = cxl_region_attach_position(cxlr, cxlrd, cxled,
-							dport, i);
+			rc = cxl_region_attach_position(cxlr, cxled, dport, i);
 			if (rc)
 				return rc;
 		}
@@ -2100,7 +2099,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 	if (rc)
 		return rc;
 
-	rc = cxl_region_attach_position(cxlr, cxlrd, cxled, dport, pos);
+	rc = cxl_region_attach_position(cxlr, cxled, dport, pos);
 	if (rc)
 		return rc;
 
@@ -2396,8 +2395,8 @@ static const struct attribute_group *region_groups[] = {
 
 static void cxl_region_release(struct device *dev)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
 	struct cxl_region *cxlr = to_cxl_region(dev);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	int id = atomic_read(&cxlrd->region_id);
 
 	/*
@@ -2480,10 +2479,12 @@ static struct cxl_region *cxl_region_alloc(struct cxl_root_decoder *cxlrd, int i
 	 * region id allocations
 	 */
 	get_device(dev->parent);
+	cxlr->cxlrd = cxlrd;
+	cxlr->id = id;
+
 	device_set_pm_not_required(dev);
 	dev->bus = &cxl_bus_type;
 	dev->type = &cxl_region_type;
-	cxlr->id = id;
 	cxl_region_set_lock(cxlr, &cxlrd->cxlsd.cxld);
 
 	return cxlr;
@@ -3115,7 +3116,7 @@ EXPORT_SYMBOL_FOR_MODULES(cxl_calculate_hpa_offset, "cxl_translate");
 u64 cxl_dpa_to_hpa(struct cxl_region *cxlr, const struct cxl_memdev *cxlmd,
 		   u64 dpa)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_region_params *p = &cxlr->params;
 	struct cxl_endpoint_decoder *cxled = NULL;
 	u64 dpa_offset, hpa_offset, hpa;
@@ -3168,7 +3169,7 @@ static int region_offset_to_dpa_result(struct cxl_region *cxlr, u64 offset,
 				       struct dpa_result *result)
 {
 	struct cxl_region_params *p = &cxlr->params;
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_endpoint_decoder *cxled;
 	u64 hpa, hpa_offset, dpa_offset;
 	u16 eig = 0;
@@ -3522,7 +3523,7 @@ static int match_region_by_range(struct device *dev, const void *data)
 static int cxl_extended_linear_cache_resize(struct cxl_region *cxlr,
 					    struct resource *res)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_region_params *p = &cxlr->params;
 	resource_size_t size = resource_size(res);
 	resource_size_t cache_size, start;
@@ -3558,9 +3559,9 @@ static int cxl_extended_linear_cache_resize(struct cxl_region *cxlr,
 }
 
 static int __construct_region(struct cxl_region *cxlr,
-			      struct cxl_root_decoder *cxlrd,
 			      struct cxl_endpoint_decoder *cxled)
 {
+	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
 	struct range *hpa_range = &cxled->cxld.hpa_range;
 	struct cxl_region_params *p;
@@ -3656,7 +3657,7 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
 		return cxlr;
 	}
 
-	rc = __construct_region(cxlr, cxlrd, cxled);
+	rc = __construct_region(cxlr, cxled);
 	if (rc) {
 		devm_release_action(port->uport_dev, unregister_region, cxlr);
 		return ERR_PTR(rc);

drivers/cxl/cxl.h

@@ -529,6 +529,7 @@ enum cxl_partition_mode {
  * struct cxl_region - CXL region
  * @dev: This region's device
  * @id: This region's id. Id is globally unique across all regions
+ * @cxlrd: Region's root decoder
  * @mode: Operational mode of the mapped capacity
  * @type: Endpoint decoder target type
  * @cxl_nvb: nvdimm bridge for coordinating @cxlr_pmem setup / shutdown
@@ -542,6 +543,7 @@ enum cxl_partition_mode {
 struct cxl_region {
 	struct device dev;
 	int id;
+	struct cxl_root_decoder *cxlrd;
 	enum cxl_partition_mode mode;
 	enum cxl_decoder_type type;
 	struct cxl_nvdimm_bridge *cxl_nvb;